共查询到20条相似文献，搜索用时 31 毫秒
1.
V. V. Prokofieva-Mikhailovskaia A. N. Rublevskii 《Kinematics and Physics of Celestial Bodies》2013,29(5):247-253
Vesta’s crater sizes that are based on images returned from the Dawn probe orbiting the asteroid 4 Vesta are compared with sizes of spots on its surface derived from hydrosilicate equivalent widths and asteroid color indices B-V and V-R observed spectrophotometrically on earth using a spectral-frequency method. The sizes of craters and spots at the asteroid poles prove to correspond to the sizes of spots that are assumed to be located at latitudes of 40°...45° N and S. Comparative results for the crater sizes ranging from 10 to 100 km are tabulated. We conclude that crater sizes on asteroid surfaces can be determined using the spectral-frequency method. 相似文献
2.
Photoelectric magnitudes and colors on the UBV system are presented for 65 minor planets, including four Mars crossers, six Trojans, and main-belt objects down to 6 km in diameter. The Trojans all have very similar colors not characteristics of the main-belt population. A paucity of S-type asteroids at the smallest diameters, predicted from trends seen at larger sizes, is not observed. The newly available color data for small objects ranging from 1.0 to 5.2 AU in heliocentric distance show the main belt to be a transition zone between predominantly silicate and carbonaceous compositions. 相似文献
3.
The space mission of the laser ranging of asteroid Icarus is that a laser reflector and a timer are placed on the No.1566 asteroid and the laser interference ranging is conducted between the asteroid and the ground-based station for making the precise measurements of the PPN parameters γ and β, solar quadrupolar moment J2, time rate of change ?/G of the gravitational constant and barycentric gravitational constant of the solar system objects. With the development of laser techniques, the timing accuracy of 10 ps (or 3 mm expressed by the amount of ranging) can be realized. In 2015 the asteroid Icarus will be close to the earth, which provides a better launch window for the Icarus lander. In the present article the 2003 interplanetary ephemeris frame of the PMOE is adopted to simulate the laser ranging between the ground-based station and the asteroid for 800 days from 2015 September 25 on and obtain the indeterminacies of 18 parameters, among which those of γ, β, J2 and ?/G are respectively 7.8 × 10−8, 9.0 × 10−7, 9.8 × 10−11 and 7.0 × 10−15yr−1, with each being 1 to 3 orders higher than the available experimental accuracy. The simulated result shows that this space mission is of scientific significance to the test of the theory of relativity, determination of the fundamental parameters of solar system and test of the space-time fundamental laws. 相似文献
4.
Voyager imaging observations provide new photometric data on Saturn's satellites at large phase angles (up to 133° in the case of Mimas) not observable from Earth. Significant new results include the determination of phase integrals ranging from 0.7 in the case of Rhea to 0.9 for Enceladus. For Enceladus we find an average geometric albedo pv = 1.04 ± 0.15 and Bond albedo of 0.9 ± 0.1. The data indicate an orbital lightcurve with an amplitude of 0.2 mag, the trailing side being the brighter. For Mimas, the lightcurve amplitude is probably less than 0.1 mag. The value of the geometric albedo of Mimas reported here, pv = 0.77 ± 0.15 (corresponding to a mean opposition magnitude V0 = +12.5) is definitely higher than the currently accepted value of about 0.5. For Dione, the Voyager data show a well-defined orbital lightcurve of amplitude about 0.6 mag, with the leading hemisphere brighter than the trailing one. 相似文献
5.
《Chinese Astronomy and Astrophysics》1982,6(3):225-232
The extended Kalman filter is used in this paper to process single-station laser ranging data over a few revolutions to improve the satellite orbit. The aim is to provide accurate short-term predictions of the satellite position. The dynamical model includes the perturbations due to the Earth's oblateness, air drag, solar radiation pressure and the gravitational attractions of the Sun and the Moon.The proposed method is tested with simulated and real LAGEOS data. The results show that the above aim is achievable. Moreover, the computing program based on the present method can be realized on mini-computers. 相似文献
6.
Rulee Baruah Kalpana Duorah H. L. Duorah 《Journal of Astrophysics and Astronomy》2009,30(3-4):165-175
The rapid neutron capture process (r-process) is one of the major nucleosynthesis processes responsible for the synthesis of heavy nuclei beyond iron. Isotopes beyond Fe are most exclusively formed in neutron capture processes and more heavier ones are produced by the r-process. Approximately half of the heavy elements with mass number A > 70 and all of the actinides in the solar system are believed to have been produced in the r-process. We have studied the r-process in supernovae for the production of heavy elements beyond A = 40 with the newest mass values available. The supernova envelopes at a temperature >109 K and neutron density of 1024 cm?3 are considered to be one of the most potential sites for the r-process. The primary goal of the r-process calculations is to fit the global abundance curve for solar system r-process isotopes by varying time dependent parameters such as temperature and neutron density. This method aims at comparing the calculated abundances of the stable isotopes with observation. We have studied the r-process path corresponding to temperatures ranging from 1.0 × 109 K to 3.0 × 109 K and neutron density ranging from 1020 cm?3 to 1030 cm?3. With temperature and density conditions of 3.0 × 109 K and 1020 cm?3 a nucleus of mass 273 was theoretically found corresponding to atomic number 115. The elements obtained along the r-process path are compared with the observed data at all the above temperature and density range. 相似文献
7.
J.O. Oyinloye 《Planetary and Space Science》1973,21(6):889-890
A method of analysis of blanketing Es data, based on an empirical formula proposed by Smith (1957), is outlined and it is shown that fbEs data can be fitted well by the empirical formula. The empirical method of analysis can provide information on occurrence frequency of Es- layers with fbEs less than foE.Results obtained from empirical analysis of data from Ibadan and Port Stanley indicate that (i) observed time variation of mean is influenced considerably by the choice of the lower limiting frequency used for the Es count and (ii) that blanketing Es-layers observable at equatorial latitudes could be of comparable intensity as those observable at midlatitudes, though blanketing Es is more frequent at midlatitudes. 相似文献
8.
Theoretical physical models of the Martia interior are presented in the light of new and revised data and constraints. These models include thermal evolution, densities, and seismic wave velocities. The interior of Mars appears to be Earth-like in many respects. Although thermal models indicate that Mars has passed its peak of evolution it may still have an asthenosphere and may be moderately active tectonically. Mars has an Fe-FeS core with a radius of and may be moderately active tectonically. Mars has an Fe-FeS core with a radius of 1500–2000 km. The mantle is enriched in FeO with an olivine composition of about Fo75. Theoretically determined seismic wave velocities are relatively well constrained in the mantle with upper-mantle Pn velocities ranging from 7.64 to 7.80 km/sec. However, there are wide variations in VP in the core dependent on composition. The shadow zone due to the core is larger than the Earth's. 相似文献
9.
The relief of polygonal structures at the Phoenix landing site on Mars has been determined with the improved photoclinometry method from the images acquired with the HiRISE camera on board the Mars Reconnaissance Orbiter. The investigations showed that, within 1 km from the landing site, the topography amplitude of the relief on the surface scales of 5.5–65 m varies within the range of ～40 to 70 cm. The polygonal structures of 2–6 m across correspond to the small-scale relief with the topography amplitude ranging from 20 to 30 cm and the standard deviation of about 3 cm. Within 1 km from the landing site, the variations of these characteristics are small. For the small polygons that are less than 5.5 m in size, the typical height is 10–15 cm. The polygons of 18–22 m in size are up to 28 cm in height, while the polygons of 60–90 m in size reach about 44 cm in height. The error in determining the relief heights was ±5.5%. The investigations showed that the improved photoclinometry method is promising for the study of small-scale features of the Martian surface. 相似文献
10.
Clay mineral-bearing deposits previously discovered on Mars with near infrared (λ=0.3-5 μm) remote sensing data are of major significance for understanding the aqueous history, geological evolution, and past habitability of Mars. In this study, we analyzed the thermal infrared (λ=6-35 μm) surface properties of the most extensive phyllosilicate deposit on Mars: the Mawrth Vallis area. Clay mineral-bearing units, which in visible images appear to be relatively light-toned, layered bedrock, have thermal inertia values ranging from 150 to 460 J m−2 K−1 s−1/2. This suggests the deposits are composed of a mixture of rock with sand and dust at 100-meter scales. Dark-toned materials that mantle the clay-bearing surfaces have thermal inertia values ranging from 150 to 800, indicating variable degrees of rockiness or induration of this younger sedimentary or pyroclastic unit. Thermal Emission Spectrometer (TES) spectra of the light-toned rocks were analyzed with a number of techniques, but none of the results shows a large phyllosilicate component as has been detected in the same surfaces with near-infrared data. Instead, TES spectra of light-toned surfaces are best modeled by a combination of plagioclase feldspar, high-silica materials (similar to impure opaline silica or felsic glass), and zeolites. We propose three hypotheses for why the clay minerals are not apparent in thermal infrared data, including effects due to surface roughness, sub-pixel mixing of multiple surface temperatures, and low absolute mineral abundances combined with differences in spatial sampling between instruments. Zeolites modeled in TES spectra could be a previously unrecognized component of the alteration assemblage in the phyllosilicate-bearing rocks of the Mawrth Vallis area. TES spectral index mapping suggests that (Fe/Mg)-clays detected with near infrared data correspond to trioctahedral (Fe2+) clay minerals rather than nontronite-like clays. The average mineralogy and geologic context of these complex, interbedded deposits suggests they are either aqueous sedimentary rocks, altered pyroclastic deposits, or a combination of both. 相似文献
11.
The traditional least square estimation (LSE) method for orbit determination will not be optimal if the error of observational data does not obey the Gaussian distribution. In order to solve this problem, the least p-norm (Lp) estimation method is presented in this paper to deal with the non-Gaussian distribution cases. We show that a suitable selection of parameter p may guarantee a reasonable orbit determination result. The character of Lp estimation is analyzed. It is shown that the traditional Lp estimation method is not a robust method. And a stable Lp estimating based on data depth weighting is put forward to deal with the model error and outlier. In the orbit determination process, the outlier of observational data and coarse model error can be quantitatively described by their weights. The farther is the data from the data center, the smaller is the value of data depth and the smaller is the weighted value accordingly. The result of the new Lp method is stabler than that of the traditional Lp estimation and the breakdown point could be up to 1/2. In addition, the orbit parameter is adaptively estimated by residual analysis and matrix estimation method, and the estimation efficiency is enhanced. Finally, by taking the Space-based Space Surveillance System as an example and performing simulation experiments, we show that if there are system error or abnormal value in the observational data or system error in satellite dynamical model and space-based observation platform, LSE will not be optimal even though the observational data obeys the Gaussian distribution, and the orbit determination precision by the self-adaptive robust Lp estimation method is much better than that by the traditional LSE method. 相似文献
12.
Using a method defined in a previous paper [M. Combes and T. Encrenaz, Icarus39 1–27 (1979)], we reestimated the C/H ratio in the atmospheres of Jupiter and Saturn by the measurements of the weak visible CH4 bands, the CH4 3ν3 band, and the (3-0) and (4-0) quadrupole bands of H2. In the case of Jupiter we conclude that the C/H ratio is enriched by a factor ranging from 1.7 to 3.6 relative to the solar value. In the case of Saturn, our derived C/H value ranges from 1.2 to 3.2 times the solar value. The Jovian D/H ratio derived from this study is 1.2 × 10?5 < D/H < 3.1 × 10?5. The value derived for the D/H ratio on Saturn is not precise enough to be conclusive. 相似文献
13.
We present a new code (companion) that identifies bound systems of particles in O(NlogN) time. Simple binaries consisting of pairs of mutually bound particles and complex hierarchies consisting of collections of mutually bound particles are identifiable with this code. In comparison, brute force binary search methods scale as O(N2) while full hierarchy searches can be as expensive as O(N3), making analysis highly inefficient for multiple data sets with N?103. A simple test case is provided to illustrate the method. Timing tests demonstrating O(NlogN) scaling with the new code on real data are presented. We apply our method to data from asteroid satellite simulations [Durda et al., 2004. Icarus 167, 382-396; Erratum: Icarus 170, 242; reprinted article: Icarus 170, 243-257] and note interesting multi-particle configurations. The code is available at http://www.astro.umd.edu/zoe/companion/ and is distributed under the terms and conditions of the GNU Public License. 相似文献
14.
On the basis of assumed photospheric temperature models for 36 extreme supergiants (logg e -values of 1, 0.5 and 0;T e ranging from approx. 3700–33 000 K) photospheric fluxesS(τλ) were computed for 36 wavelengths ranging from 100 Å to 60 000 Å. The hot models are in perfect radiative equilibrium; the cooler show deviations up to 10%, sometimes even larger. Only in the relatively deep parts of the photospheres (τ5?1) the radiation field at each geometrical level can be characterized by one unique radiation temperature; for smaller τ5-values there are large deviations from local thermal equilibrium. The influence of deviations from local thermodynamical equilibrium on the fluxes is briefly examined, and appears small but for the shortest wavelengths. In tables and graphs we give for these models πF(γ)-values, integrated fluxes, effective temperatures, coloursU, B andV, and the Balmer discontinuityD. 相似文献
15.
Martin Pätzold Matthias Hahn Silvia Tellmann Bernd Häusler Michael K. Bird G. Leonard Tyler Sami W. Asmar Bruce T. Tsurutani 《Solar physics》2012,279(1):127-152
Coronal radio-sounding experiments were carried out using the S-band (2.3 GHz) and X-band (8.4 GHz) signals of the ESA Mars Express, Venus Express, and Rosetta spacecraft during five superior conjunctions occurring in 2004, 2006 (3×), and 2008/2009. Differential frequency and propagation delay (ranging) observations were recorded during these opportunities over the better part of a solar cycle, yielding information on the large-scale structure of the coronal electron-density distribution and its variations, including fluctuations on time scales from seconds to hours. These results concern primarily regions of slow solar wind because the radio propagation path is generally confined to the low heliolatitude regions by the conjunction. The mean frequency fluctuation and total electron content are determined as a function of heliocentric distance, and, with a few exceptions caused by streamers and CMEs, are found to be consistent with previous results from experiments on Ulysses. Dense coronal streamers and several coronal mass ejection (CME) events were identified in the radio-frequency data, some of which were observed in white light by the LASCO coronagraphs onboard SOHO. For those events with sufficient mutual coverage, good correlations are found between the electron-content fluctuations and structure imaged by the LASCO instrument. 相似文献
16.
The University of Texas McDonald Observatory has long been a pioneer in acquiring laser ranging data, a data type which has substantially improved our knowledge of the dynamics of the earth-moon system as well as various aspects of geophysics and general relativity. (See Mulholland, 1980; Shelus, 1985; Shelus, 1987.) The McDonald Laser Ranging System (MLRS) is one of only 2 laser ranging stations world-wide having the capability of routine data acquisition on both lunar and artificial satellite targets (Shelus,IEEE, 1985). In this paper we discuss the current applications of modern computer technology to the problems of acquiring and reducing that ranging data. As technology continues to improve, the logical upgrade is the replacement of obsolescent station minicomputers with the resource-rich environment of micro-computers. The goal is to allow the automation of many station ranging functions as well as the enhancement of onsite data quality control, filtering, and analysis. Plans for such upgrades and their implications for dynamical astronomy are discussed. 相似文献
17.
According to the data of optical observations of the Tuorla Observatory in Finland, using the power spectrum method, DCF (Discrete Correlation Function) method, and Jurkevich method, respectively, we analyzed the periodicity of the long-term light variation of the BL Lac object 1ES 1959+650, and obtained its light period to be P =1.4±0.3 yr. Assuming that the origin of the periodicity is concerned with the accretion disk, we obtained the region where the instability of this source occurs being R =9.65 Rg, here Rg represents the Schwarzschild radius. 相似文献
18.
Bistatic radar observations of Mars' north polar region during 1977–1978 showed surface rms slope σβ ranging from 1 to 6°; these values apply to horizontal scales of 1–100 m. Values of roughness tend to decrease with increasing latitude (especially over 65–80°N), but there are many exceptions. The smoothest surfaces (σβ≤1°) appear to be inclusions within generally rougher (σβ～3°) terrain, rather than broad expanses of very smooth material. The permanent north polar cap is relatively uniform with 2.5?σβ?3.0°. Considerable structure has been found in echo spectra, indicating a heterogeneous and perhaps anisotropic scattering surface. Echo spectra obtained from the same region, but several months apart (1°<LS<62°), show no significant differences in inferred roughness. Estimates of reflectivity and dielectric constant are systematically low in the polar region. This may indicate that surface material north of 65°N is less dense than that near the equator, but more study of these data is needed. Estimates of surface roughness and dielectric constant in the equatorial region are consistent with results from Earth-based measurements to the accuracy of our analysis. 相似文献
19.
Ayesha Anjum Mousumi Das Jayant Murthy S. B. Gudennavar Rajesh Gopal S. G. Bubbly 《Journal of Astrophysics and Astronomy》2018,39(5):61
We have classified a sample of 37,492 objects from SDSS into QSOs, galaxies and stars using photometric data over five wave bands (u, g, r, i and z) and UV GALEX data over two wave bands (near-UV and far-UV) based on a template fitting method. The advantage of this method of classification is that it does not require any spectroscopic data and hence the objects for which spectroscopic data is not available can also be studied using this technique. In this study, we have found that our method is consistent by spectroscopic methods given that their UV information is available. Our study shows that the UV colours are especially important for separating quasars and stars, as well as spiral and starburst galaxies. Thus it is evident that the UV bands play a crucial role in the classification and characterization of astronomical objects that emit over a wide range of wavelengths, but especially for those that are bright at UV. We have achieved the efficiency of 89% for the QSOs, 63% for the galaxies and 84% for the stars. This classification is also found to be in agreement with the emission line diagnostic diagrams. 相似文献
20.
Lightcurves of 433 Eros are reported for 11 bandpasses ranging from 0.65 to 2.2 μm in wavelength. The relative spectral reflectance, R(λ), was not seen to vary during our observations. Eros has R(1.6 μm) = 1.5 ± 0.1 and R(2.2 μm) = 1.7 ± 0.1, where R(λ) is the spectral reflectance scaled to unity at λ = 0.56 μm. This spectral reflectance is suggestive of a mixture of silicates and material with high infrared reflectance, perhaps a metallic phase such as meteoritic “iron”. 相似文献